The present invention pertains in general to overcurrent protection circuits and methods therefor and more particularly to overcurrent protection circuits for multiple output switching power supplies and methods therefor.
In a multiple output power supply each output may not be designed to handle the total power output. However, when an output is shorted, the power supply will deliver most of the total power to the shorted output. This means that for each shorted output, a rectifier diode, commonly placed in series with the output, must dissipate the total power. Such a diode can commonly withstand a short circuit for about 5 to 10 seconds, after which it fails due to excessive heat buildup. Thus, the key to protecting the rectifier diodes is to limit the average power dissipation in the diodes during a short.
One approach to limiting power dissipation is to place an overcurrent protection circuit in each output. One type of overcurrent protection circuit limits the current in the diode on a cycle-by-cycle basis. Another type of overcurrent protection circuit limits the average current in the diode by blanking the power supply during a short circuit. In either type of circuit, a current limiter is placed in each output.
It is desirable from the standpoint of limiting the number of parts, the amount of space required and the cost for a power supply to have a single overcurrent protection circuit for a multiple output switching power supply.